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Servicing transmission and overdrive

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drooartz

drooartz

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So it's time to do a drain and refill on the transmission and overdrive. I've got oil for the box (same VR1 20W50 racing I use in the engine -- easier to just use the same stuff) but wondering what else I need.

There's a filter(?) in the OD unit -- replace? Drain plug gaskets? Anything else? I'm putting in a Moss order and don't want to forget anything.
 
Drew, how's everything working now? Does the OD work ok? If these answers are yes, then it's a straight forward job. I'd just drain old out and refill. The MGB transmission is pretty bullet proof and if their working correctly, I don't fool with them. I'll probably get some flack on this, but if the transmission is quiet while shifting, I change oil in them when I see a darkening of the oil, which is rare. JMHO. PJ
 
Everything seems to be working fine. Transmission shifts fine, no issues there. OD takes a moment to engage, but disengages quickly. Leaks a bit, but that's not too surprising I guess. Not horrible, I just check the dipstick every now and then (it's usually fine).

I don't know if/when the OD was ever drained/cleaned/filter replaced (there is a filter, correct? Moss shows something). As the car is still relatively new to me (1 year) I'd like to have some piece of mind knowing that it's been taken care of.
 
If it ain't broke ------. Been there done that. Be aware that there are several plugs under the transmission that look like drain plugs. Some aren't. At least one of them contains a check ball and can be lost in an instant. Proceed carefully. Bob
 
If you change the filter its behind the 2"x3" plate on the bottom of the trans. There are 6 small bolts holding it on. Be sure not to overtighten these and break them off. Dirt of grit can be a big problem with a overdrive. Be sure your funnel and the area around the fill plug are clean so nothing but oil goes in. Bob
 
Thanks guys. I'll check back in before I tackle this one and make sure I've identified the proper drain plugs and such.
 
Only one drain plug on a later overdrives required to drain. Its the one closest to the engine. Its not close to the overdrive but will drain the overdrive since its at the lowest point on the trans. As I recall it takes a 11/16 or 3/4 inch wrench to remove it. Have a good scraper to get the screen/filter off under that 6 bolt cover. Do not remove the small cover with the wire coming out of it. That one has the little ball that can drop out and be lost forever. I use 30 wt non detergent oil in overdrives. Check Quantum Mechanics website for his advise on oils. Bob
 
Thanks, Bob.
 
Hi Drew!

Don't want to inject confusion or delay - but I've messed up (in the past) by using incorrect oil in my OD gearbox. I am not familiar with VR1 20W50 racing oil; but the oil needs to be "normal" (non-synthetic) and non-detergent. After putting in oil that didn't meet these criteria, my OD stopped working - so I had to "rinse" with several changes of correct oil until everything worked perfectly again. I think the manual for my '72 calls out for straight 30W non-detergent. I had to do a little searching until I found that exact oil (it's now so archaic that it's no longer common in my neck of the woods). However, now everything works perfectly! I don't think you can go wrong using the manufacturer-specified weight and grade; though some may argue that you might be able to do better by using something else.

Good luck!

Phil
 
The VR1 is a non-detergent oil -- it's what I used in the Sprite box as well. Haven't done a full drain on this gearbox since I bought the car last year, just topped it off occasionally. Straight 30W is what Quantum Mechanics recommends, though the owner's manual says to use what you use in the engine (20W50 is one of the recommended weights).

I'll see what I can find before I do the service. There's no rush as it's working okay now.
 
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